This invention relates to the field of separating hydrogen fluoride (HF) from organics.
A majority of fluorochemicals of commercial interest, including chlorofluorocarbons (CFC's), hydrogen-containing chlorofluorocarbons (HCFC's), hydrogen-containing fluorocarbons (HFC's) and perfluorocarbons (FC's), are manufactured by using halogen-exchange reactions. Generally, in these reactions, the appropriate chlorocarbon is reacted with a fluorine-containing compound which serves as the fluorine source. Usually, the fluorine source is HF and it is used in the presence of various catalytic compounds. This halogen-exchange reaction may be illustrated by considering the preparation of monochlorodifluoromethane (HCFC-22); in this illustration, chloroform is the chlorocarbon employed and HF is the fluorine source. ##STR1##
The catalysts that are useful in this reaction include various metal oxides and halides and the reaction can be carried out in either vapor or liquid phase. The amount of HF which is used in the above illustrated reaction is almost always in excess of the stoichiometric amount and may be present in as much as a ten-fold excess. Excess HF is used to increase yields and conversions and to reduce the reaction time. In the reaction illustrated by Equation(1), the crude reaction stream may contain some unreacted CHCl.sub.3, under-fluorinated CHCl.sub.2 F, the desired CHClF.sub.2, by-product hydrogen chloride (HCl) and unreacted HF. By the use of a combination of art-known processes, such as distillation, phase separation and the like, HCl can be recovered as useful anhydrous HCl, CHCl.sub.3 and CHCl.sub.2 F can be recovered, and most of the HF can be recovered. The CHCl.sub.3, CHCl.sub.2 F and the HF may then be used for other purposes or recycled. However, the desired product, CHClF.sub.2 (HCFC-22), cannot be recovered by distillation completely free of HF because HCFC-22 and HF form an azeotropic mixture and such mixtures are not amenable to separation by ordinary distillation.
An object of the present invention is to provide an effective, economical, and easily installed process for separating HF from organics, including the separation of HF and organics which form azeotropic or azeotrope-like mixtures. Another object of the present invention is to provide a process for separating and recovering the components of a mixture of HF and an organic composition so that waste product disposal problems/costs are avoided and/or reduced. Another object is to provide a process for recovering HF in substantially anhydrous form which may be directly recycled as a process reactant. Another object is to provide a process which avoids the necessity of deacidifying mixtures containing HF using aqueous scrubbing techniques which can cause the formation of unwanted impurities. A further object is to provide a separation process for a mixture of HF and organics which results in obtaining the individual components of the mixture in essentially pure forms.
These and other objects of the invention will be clear from the description of the invention provided herein.